BIOL 3150 Lab 4 and 5.pdf

BIOL 3150 Lab 4 and 5.pdf - LABORATORY 4 – FOOD...

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47 LABORATORY 4 FOOD MICROBIOLOGY AND MICROBIAL GENETICS EXERCISE 1: Microbial Genetics (Part 1) DNA IDENTIFICATION OF MYCOPLASMA Introduction: The Bacterium Mycoplasma The bacterial genus Mycoplasma is an extremely small group of bacteria ranging in size from 0.1 to 0.5 μm. They were once thought to be a viral entity due to their small size and pliable structure. They have a very small genome (around 500 genes on a genome of ~ 500kbp). This is perhaps the smallest genome of all pathogenic bacteria. Mycoplasma naturally lack a cell wall which leads to a few of cellular structural differences between these bacteria and most others. The cell exterior is more pliab le and consequently they don’t demonstrate one consistent shape when viewed in a microscope (coccoid to rod to dumbbell to various others) and so are considered to be Pleomorphic. Other cell wall containing bacteria can also be pleomorphic but for different reasons. In theory, lacking a peptidoglycan layer should make the cell exterior weak and likely to burst. To increase stability, Mycoplasma have cholesterol in their cell membrane and so are resistant to lysis. Cholesterol isn’t normally found in bacteri a in fact it is found in animal cell membranes only. Lipoglycans (similar to LPS without the Lipid A portion) can be found on the outer membrane. These help to stabilize the membrane and to aid in attachments to host cells. The most medically significant member of this genus is Mycoplasma pneumonia which is the primary pathogen that causes “Walking Pneumonia”. The bacteria adhere to epithel ial cells of the lung and cause some breathing discomfort but not to the level of influenza infected hosts can continue their normal lives (hence the name). This is considered to be an atypical form of pneumonia. This type of pneumonia is the most common type found in high school and college aged people. Walking pneumonia is generally treated with tetracyclines however it takes a fairly long cycle to eradicate the bacteria from the host and the host (who may not be symptomatic) is still infective (aerosols). Mycoplasmas (not just M. pneumoniae ) are a very common contaminant of animal cell cultures. They can Objectives for Week 4 - After completing these exercises, you should: 1. Know how to analyze food for microbial contamination (microbial load). 2. Use differential/selective media to isolate putative enteric bacteria (coliforms) from food. 3. Understand and use DNA technology to identify microorganisms. 4. Transform E. coli cells with an R-plasmid by heat-shock.
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